Actually exit the function if dataset is not resizable

[lawrence-mbf]

Motivation

H5D might actually still fail even if a warning is emitted. Should actually exit to not risk breaking writes since we shouldn't be writing anyway.

How to test the behavior?

Attempt to modify a pynwb-generated file. You might (or might not) actually encounter the error with /file_create_date

Checklist

• [x] Have you ensured the PR description clearly describes the problem and solution?
• [x] Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• [x] If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[codecov[bot]]

Codecov Report

Merging #551 (9177afe) into master (5d813aa) will decrease coverage by 0.05%. The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #551      +/-   ##
==========================================
- Coverage   87.82%   87.78%   -0.05%     
==========================================
  Files         132      132              
  Lines        5628     5631       +3     
==========================================
  Hits         4943     4943              
- Misses        685      688       +3     

Files	Coverage Δ
+io/writeDataset.m	83.33% <83.33%> (-7.58%)	:arrow_down:

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